The present invention relates to vacuum chambers. More particularly, the present invention relates to an improved vacuum chamber in a plasma processing device.
Vacuum chambers may be used in manufacturing. Vacuum chambers may be used for plasma processing.
To facilitate discussion, FIG. 1 is a schematic view of a prior art vacuum chamber 10 used in a plasma processing process. The vacuum chamber 10 may have a chamber wall 12, a bottom 14, a cover 16 and at least one exhaust port 18 to remove gas from the vacuum chamber to maintain a vacuum. The cover 16 may be mounted on the chamber wall 12 with a seal 22 between the cover 16 and the chamber wall 12 to help maintain the vacuum. The cover 16 may be supported around the edge of the cover with no support in the middle. In a plasma processing device that capacitively establishes a plasma, a lower electrode 24 may be supported by the bottom 14, and an upper electrode 26 may be supported by the cover. Such plasma processing devices may require a uniform spacing between the upper electrode 26 and the lower electrode 24. The vacuum load may cause the cover 16 to deform, as indicated by dashed lines 28 in FIG. 1. Since the upper electrode 26 is supported by the cover 16, the deformation of the cover 16 may cause the upper electrode 26 to deform, as indicated by dashed line 30. The deformation of the upper electrode 26 may cause the spacing between the upper electrode 26 and the lower electrode 24 to not be uniform. If the upper electrode 26 or some other critical element fastened to more than one point on the cover is brittle, the deformation may crack the upper electrode or other critical element. A critical element is defined as a device such as the upper electrode or an antenna, supported by the cover 16, which is affected by the deformation of the cover.
As larger wafers are being processed in plasma devices using vacuum chambers, larger vacuum chambers are required. Wider diameters of the larger covers may cause the larger covers to be more susceptible to deformation under a vacuum load.
To avoid deformation, the covers may be made thicker, which makes the covers heavier and more expensive.
In view of the foregoing, it is desirable to a vacuum chamber cover that remains flat in vacuum conditions.